A Drill Metal Cutter

[labhras773]

Hi everyone, new to this forum and craft, so feel free to advise and critique away.
Attached photo is a mock-up of what I have in mind to build. It's a drill operated metal cut-off tool. I've got it to what i want it to look like and now I'm stumped.
1 - At present I'm using scrap Aluminium box sections on the mock-up, for the real unit can I still use aluminium or would steel be better?
2 - Any suggestions on a blade guard -material -fastening?

I do not have a welder, so I'm going to be either using rivets or bolts, so any feedback on those also very much appreciated.